Magnetohydrodynamic generator



F1 F85 O 2 May 9, 1967 5 J, m JR" ET AL 3,319,092

MAGNETOHYDRODYNAMIC GENERATOR 2 Sheets-Sheet 1 Filed Oct. 2'7, 1964 M a WMMM; wwwfi M M WW WWW May 9. 9 s. J. KEATING, JR.. ET AL 1 MAGNETOHYDRIODYNAYMIC GENERATOR Filed Oct. 27, 1964 2 Sheets-Sheet 2 United States Patent 3,319,092 MAGNETOHYDRODYNAMIC GENERATOR Stephen J. Keating, Jr., West Hartford, and Donald H. Wood, Glastonbury, Conn., assignors to the United States of America as represented by the Secretary of the Air Force Filed Oct. 27, 1964, Ser. No. 406,952 4 Claims. (Cl. 310-11) This invention relates generally to magnetohydrodynamic power generators and, more particularly, to an insulating side wall design for the generator channel.

There are extreme conditions encountered in MHD generators where velocities approach 6500 feet per second, plasma temperatures range from 4500 to 57-00 R., heat flux is approximately 1-00 to 300 B.t.u. per square foot per second, the flow is highly reactive and high voltage gradients are present. The design parameters require the optimum structural performance in order to produce a practical generator.

Because of the very high electrical fields present in the MHD channel, electrically non-conducting sidewalls must be used. Tests have shown that ceramic-coated metal walls are not satisfactory in the severe environment. Thus, relatively thick ceramic blocks must be used as the liner. These materials are, however, extremely brittle and sensitive to thermal stress.

The nature of the parameters require high temperature walls to minimize deposition of electrically conducting salts from the plasma on the walls. These high temperature walls require use of refractory ceramics in a manner providing high resistance to thermal stress. Thus, it is indicated that controlled compression and redundant supports are required in order to compensate for the low thermal stress resistance and tensile strength of present day ceramics. The maintenance of electrical integrity of an MHD generator for an extended period of time requires that cracking of the ceramic be minimized since condensed seeding material and other plasma constituents collect in the cracks and lessen the effectiveness of the insulating properties.

High density, high purity, hot-pressed beryllium oxide was found to be the best material for an MHD generator side wall except for its resistance to thermal stress.

The design of this invention allows for expansion, warping and moving of the ceramics during the transient warm up period and during running by keeping all pieces in compression, failure due to tension induced by thermal stress is avoided. Thus, the instant design eliminates the thermal stress and thermal shock disadvantage of the brittle and hard ceramic materials. Motion of all ceramic pieces is permitted with thermal expansions while springs exert compression forces on the beryllia side wall pieces. Angles provided on the ends of the side wall pieces transmit the loading for compressive forces. Thermal expansion, therefore, merely increases the compressive loading. Axial expansion is permitted since each side wall module is sprung independently and actual clearance is provided in assembly.

Redundancy is provided by interlocking the side wall pieces; therefore, a piece, which might crack, would be held in place by the side wall pieces adjacent. BeO has a low coefficient of friction to permit sliding of side wall pieces. Cooling is accomplished by water flowing through a manifold arrangement.

'It is an object of this invention therefore to provide an insulating side wall for a magnetohydrodynamic generator which utilizes ceramic tiles which are held in controlled compression with redundant tongue and groove joints.

It is another object of this invention to provide an inslating side wall for a magnetohydrodynamic generator ice which has ceramic tiles arranged such that the scams or cracks between tiles are tight and crack alignment is at a 45 angle to the axis of plasma flow.

-It is still another object of this invention to provide an insulating sidewall fora magnetohydrodynamic generator which allows for maintenance of heat flow normal to the tile faces.

It is a further object of this invention to provide an insulating side wall for a magnetohydrodynamic generator which has an orientation of the underlying Water cooling passages along equipotential lines.

It is a still further object of this invention to provide an insulating side wall for a magnetohydrodynamic generator which provides for simple maintenance and replacement of modular type wall elements.

Another object of this invention is to provide an insulating side wall for a magnetohydrodynamic generator which has minimum support requirements.

Still another object of this invention is to provide an insulating side wall for a magnetohydrodynamic generator which utilizes a cooling pan in plastic or ceramic to prevent current paths to ground or adjacent pans.

A further object of this invention is to provide an insulating side wall for a magnetohydrodynamic generator which allows for operation of wall surfaces at a desired temperature of approximately 3000 R. to minimize heat loss and condensation of conductive seed salts.

A still further object of this invention is to provide an insulating side wall for a magnetohydrodynamic generator which has controlled thermal expansion of all heated surface parts by means of spring absorption in order to permit the use of refractory ceramics having an inherent brittleness and susceptibility .to temperature stress.

It is another object of this invention to provide an insulating side wall for a magnetohydrodynamic generator which provides for a ceramic tile arrangement wherein the upstream edge of all parts is protected from direct impingement of the plasma stream thereby avoiding erosion and thermal shock.

It is still another object of this invention to provide an insulating side wall for a magnetohydrodynamic generator which utilizes a tile arrangement having the leading edge surface of each piece depressed and the trailing edge slightly raised.

It is a further object of this invention to provide an insulating side wall module for an MHD generator channel which resists plasma pressures while permitting thermal expansion and which resists cracking and supersonic flutter due to the use of small ceramic pieces.

It is a still further object of this invention to provide an insulating side wall for a magnetohydrodynamic generator which is economical to fabricate with the use of conventional, currently available materials that lend themselves to mass production manufacturing techniques.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings, wherein:

FIGURE 1 is a schematic presentation of a magnetohydrodynamic generating system;

FIGURE 2 is an assembly of a series of modules which form the side wall of the MHD generator channel with portions of certain modules removed; and

FIGURE 3 is an exploded view of the side wall module.

The magnetohydrodynamic generator of this invention is designed to produce 1000 megawatts of DC. electric power for utilization in a continuous way radio frequency energy conversion system in a high power range.

Referring to 'FIGURE 1, there is shown schematically the basic components of an MHD power generation syste'm. In the system there are shown multiple combustion chambers 12 which are water-cooled and of rectangular cross-section. The combustion section converts chemical energy of the reactants to thermal energy. Each combustion chamber is connected to a converging diverging nozzle 14 to convert thermal to kinetic energy. The nozzles 14 are merged into a rectangular duct forming the entrance of the MHD generator channel 16 where kinetic energy is converted to electrical energy. The upstream end of the nozzles 14 contains nozzle splitters 20 which are insulated and provide the fine nozzle contour for transmission to the MHD generator channel 16. Injectors 18, since the temperatures obtainable with practical propellants are not high enough to ionize the combustion component sufficiently, add an easily ionizable substance, such as a potassium seed in the form of a high solution of potassium nitrate along with the propellant. The combustion chamber must provide high combustion efficiency, excellent feed distribution, low chamber surface area to reduce cooling losses and good nozzle design.

The generator channel is comprised of insulated sidewalls 22 and electrode walls at 24 which contain the electrodes 26. The insulated sidewalls must be designed not only to withstand the effect of a very hot, high velocity,-

erosive and corrosive plasma, but must also maintain essentially perfect electric integrity against a very high electric field.

Following the MHD channel there is located a diffusersplit-ter section 28 with vanes 30 therein. The end effect from the generator channel 16 can be a large source of losses due to any current induced by the combined effect of an abrupt change in magnetic field strength with axial distance and changes due to termination of the active electrodes, blooming, etc. Pressure losses are induced which must be minimized. Since magnetic fields have not been proven to be of sufficient value in reducing eddy currents, physical barriers to the eddy currents in the form of the dielectric vanes 30 are placed at the entrance and exit of the generator channel across the stream and parallel to the flow and magnetic field. At the diffuser-splitter section 28 shock waves are put to work by contouring the splitter vanes 30 to act as supersonic diffusers.

Following the section 28 is a mixer diffuser section 32 which provides a means of destroying the conductivity of the plasma before it reaches the grounded scrubber section 34.

The mixer section also serves to cool the plasma since the plasma must be scrubbed with liquid water to remove feed compound and particles eroded from the liner which would be undesirable in the exhaust. Final cooling could be achieved in the scrubbing section 34.

A magnet 36 is provided around the channel 16 to provide the magnetic field with which the plasma interacts to produce power. The magnet is required to be cooled and is maintained at cryogenic temperature by means of a liquid oxygen cooling system. A control system, not shown, capable of operating all of the components of the system would also be provided in order to complete the device.

In order to overcome the stringent requirement placed on the generator insulating sidewalls a module has been developed which fulfills all the requirements in the channel of generator section.

Referring to FIGURES 2 and 3, there are shown details of the basic module of ceramic tiles which preferably are made of beryllium oxide and are exposed to the flow of the plasma. Each module comprises a center of a generally square beryllium oxide tile which has grooves 42 on the edge surface thereof. Each side of tile 40 is engaged with one of a pair of side tiles 44 which are generally triangular in shape and when assembled form a rectangle. The side tiles 44 are provided on their hypotenuse with a groove 46 at one end which decreases and gradually becomes a tongue 48 with its maximum height at the end opposite the groove such that the tonguegroove portions of each of the beryllium oxide side tiles 44 engage with its mating tile. A tongue 43 is also provided to mate with the groove 42 in the center tile 40. The side tiles also have a bevelled portion at 48 which is arranged to engage with the tiled nozzle retaining pin 50. The tile top portion 52 of the tile retaining pin 50 has a bevel 54 therearound in order to mate with the portions 48 of side tiles 44.

The nickel retaining pin 50 is spring biased in order to provide a force on the tile. The retaining pin 50 is arranged to extend through a hole in a stainless steel cooling pan 56 for engagement with a spring retainer 62 which has a threaded portion at the base thereof. A spring 58 is interposed between the cooling pan and the spring retainer; the cooling pan 56 having a seat at 57 for this purpose. Thus, when the retaining pin is threaded into the spring retainer, the force may be varied. In order to remove the retaining pin a tool may be used to raise the pin against the biasing action of the spring and then unthread it, thereby allowing for the release of of a module.

Separation of adjacent stainless steel cooling pan 56 may be achieved by a spacer assembly 63 (as shown in FIGURE 2) which comprises boron-nitride insulators, zirconium oxide spacers and Fiber-frax insulating segments with stainless steel wave washers providing a takeup for tolerances in the elements. The particular shape and orientation of a spacer assembly may be of any conventional construction to engage the grooved sidewall portion 59 of the cooling pan 56 such that the pans are held in position.

The assembled cooling pan and spring retainer are shaped to be engaged with a cooling manifold 66 which is stepped and molded of fiberglass plastic which contains cooling passages therein. Screws 68 are provided for extension through holes in the manifold for engagement with threaded portions in a fiberglass outer wall of the generator channel section. The stepped arrangement of the manifold 66 allows for assembly of one manifold to an adjacent one; an O ring groove with an O ring 70 being provided on the mating lower portion of the stepped manifold.

Cooling is to be provided for the cooling pan by means of the passageways 71 interconnecting the steps on the manifold. In addition coolant flow holes would be provided in the spring retainer 62 adjacent to threaded portion 60, such that coolant entering the manifold would progress up through the passage 71 into stainless steel pan, down through holes in the spring seat portion 57 by the spring and through the spring retainer 62 which would then allow direction of the coolant back to the adjacent cooling manifold. The stainless steel pan 56 is arranged to fit between the upright portion 67 of the manifold and the outer edge of the coolant passage 70 at the upper step of the manifold. An 0 ring seal may be provided at 61 on the cooling pan to seal the bond of the pan against the manifold.

It should be noted that small pieces are utilized in the tiled arrangement in order to eliminate supersonic shock wave and aerodynamic flutter. When the modules are installed in the side wall, the plasma flow and the crevices formed by the joinder of the tile are arranged such that no flow would course along the crack between the tiles. In addition, all the tiles may be ramped such that the leading edges of the tiles are slightly below the edge tiles thereby eliminating erosion caused by the plasma impinging upon a raised edge. In FIGURE 2, the ramping of the pins only is shown and is exaggerated for the purpose of illustration. The upstream edge of all parts is protected from the direct impingement of the stream by depressing slightly the leading surface of each piece and raising slightly the trailing edge thereby eliminating erosion and thermal shock.

Although the invention has been described relative to a particular module embodiment, it should be understood that the particular biasing arrangement may be varied as long as the module concept is maintained with provisions for biasing and redundance. The arrangement shown could also be varied to provide for the end modules Where the sidewall meets the top or bottom wall of the generator channel. We intend to be limited only by the spirit and scope of the appended claims.

We claim:

1. A sidewall module for the generator channel of a magnetohydrodynarnic generator for joinder with similar modules comprising a general square shaped center tile of a ceramic material having the capability of Withstanding high temperatures, a pair of side tiles, said side tiles being adapted to be joined to form a generally square shape, mating tongue and groove portions on said center tile and one of said pair of side tiles for joining said side tiles with said center tile, a retaining pin, a ceramic tile secured to the top of said pin, said last mentioned tile having a beveled portion on the lower surface thereof for engagement with a mating bevel on said one of said pair of tiles, a heat conductive cooling pan having a hole therethrough for reception of said retaining pin, said pan having a spring seat therein surrounding said hole, a spring adapted to engage said seat, a spring retainer arranged to engage said spring and said pin such that variation in engagement of said pin and said spring retainer varies the force exerted by said spring on said pin, and a stepped cooling manifold having passageways therein for receipt of said cooling pan and for providing coolant to 0001 said cooling pan.

2. A module as defined in claim 1 wherein said ceramic comprises beryllium oxide.

3. A module as defined in claim 1 wherein the seams between adjacent ceramic parts lie out of parallelism with plasma flow in said generator channel.

4. A module as defined in claim 1 wherein ceramic parts are ramped with the lower edge thereof upstream of plasma fiow in said generator channel.

No references cited.

MILTON O. HIRSHFIELD, Primary Examiner. D. X. SLINEY, Assistant Examiner. 

1. A SIDEWALL MODULE FOR THE GENERATOR CHANNEL OF A MAGNETOHYDRODYNAMIC GENERATOR FOR JOINDER WITH SIMILAR MODULES COMPRISING A GENERAL SQUARE SHAPED CENTER TILE OF A CERAMIC MATERIAL HAVING THE CAPABILITY OF WITHSTANDING HIGH TEMPERATURES, A PAIR OF SIDE TILES, SAID SIDE TILES BEING ADAPTED TO BE JOINED TO FORM A GENERALLY SQUARE SHAPE, MATING TONGUE AND GROOVE PORTIONS ON SAID CENTER TILE AND ONE OF SAID PAIR OF SIDE TILES FOR JOINING SAID SIDE TILES WITH SAID CENTER TILE, A RETAINING PIN, A CERAMIC TILE SECURED TO THE TOP OF SAID PIN, SAID LAST MENTIONED TILE HAVING A BEVELED PORTION ON THE LOWER SURFACE THEREOF FOR ENGAGEMENT WITH A MATING BEVEL ON SAID ONE OF SAID PAIR OF TILES, A HEAT CONDUCTIVE COOLING PAN HAVING A HOLE THERETHROUGH FOR RECEPTION OF SAID RETAINING PIN, SAID PAN HAVING A SPRING SEAT THEREIN SURROUNDING SAID HOLE, A SPRING ADAPTED TO ENGAGE SAID SEAT, A SPRING RETAINER ARRANGED TO ENGAGE SAID SPRING AND SAID PIN SUCH THAT VARIATION IN ENGAGEMENT OF SAID PIN AND SAID SPRING RETAINER VARIES THE FORCE EXERTED BY SAID SPRING ON SAID PIN, AND A STEPPED COOLING MANIFOLD HAVING PASSAGEWAYS THEREIN FOR RECEIPT OF SAID COOLING PAN AND FOR PROVIDING COOLANT TO COOL SAID COOLING PAN. 